Typically, a reel wire type of welding device for spot welding of a vehicle has been proposed and published as Korean patent No. 337502. Such a welding device is re-formed from one according to the prior art that has an electrode fixedly inserted as a tip at a shank portion of a welding device.
In more detail, such a welding device includes a working unit, a wire, a first reel, and a second reel. The working unit includes a main body and a support portion. The wire is typically a Cr—Cu series alloy that is frequently used for spot welding. The first reel unrolls the wire and guides the wire to the working unit while the second reel rolls the wire received from the working unit. According to such a spot welding scheme, mutually contacting parts are welded by localized heating. According to such a scheme, a high current flows to overlapping plates to be welded by two overlapping welding devices through the wire.
A drawback of such a welding device occurs if tension between the two reels is lost, as the wire will become loose and unrolled. Therefore, the wire may lose direct contact with the plate such that no current flows between the wire and the plate. Welding is therefore not properly completed, and trouble may be caused by a nonconductive support portion coming into contact with the plate.